This application claims benefit of Japanese Application No. 2001-119174 filed in Japan on Apr. 18, 2001, the contents of which are incorporated this reference.
The present invention relates to a cantilever for use in Scanning Probe Microscopes (SPM), such as Atomic Force Microscopy (AFM).
Scanning Probe Microscopes (SPM) are the apparatus having a resolution of atomic order in measurement and are widely used for example to measure sample surface irregularities. In SPM, a physical quantity, such as tunnel currents or interatomic force, occurring between a probe and a sample is detected and measured. While retaining the probe and the sample at a predetermined distance from each other so as to make constant such measured quantities, the two are scanned relative to each other in the XY direction to measure a fine surface configuration of the sample. A cantilever having the probe at its terminal end is used in such measurement.
Cantilevers for such application are disclosed in Japanese patent laid-open application Hei-1-262403. FIGS. 1A to 1C are each a perspective view showing a certain part of the cantilever disclosed in the publication. Referring to FIGS. 1A to 1C, numerals 101, 103, and 105 denote a lever portion and numerals 102, 104, and 106 denote a probe portion. The cantilevers shown in FIGS. 1A and 1B have the probe portion 102 in the shape of a quadrangular pyramid or the probe portion 104 in the shape of a circular cone in the vicinity of the free end of the lever portions 101 and 103, respectively. In these cantilevers, neither of the probes 102, 104 is formed on the free end of the lever portions 101, 103. Both are formed in the vicinity of the free end. The cantilever shown in FIG. 1C, on the other hand, has the plane-like probe portion 106 at the free end of the lever portion 105.
Further, the above publication discloses an embodiment where a silicon oxide film or silicon nitride film is used as the material for the lever and probe portions. In the technique disclosed as a fabricating method of the cantilever having the quadrangular pyramid-shaped probe portion 102, gas shown in FIG. 1A, a pit is formed on a silicon substrate; a silicon oxide film or silicon nitride film to become the lever and probe portions is formed on the silicon substrate and in the pit thereof; a support portion consisting of glass is then bonded to the rear of the fixing end of the lever portion, and the silicon substrate is etched away. This method is the so-called microcast method.
Further, a cantilever disclosed in U.S. Pat. No. 5,021,364 is shown in FIG. 1D as a typical example of a cantilever having a probe portion formed by an etching process of silicon. While, as shown in FIG. 1D, a probe portion 108 is formed on the free end of a lever portion 107, the probe portion 108 is not of a film. It is provided as a bulk-like probe portion formed of a piece of silicon block.
The above described conventional cantilevers, however, have the following problems: First, of the cantilevers such as those shown in FIGS. 1A and 1B where the probe portion 102, 104 is not formed on the terminal end of the free end of the lever portion 101, 103, the probe portion is covered by the lever portion. The probe portion is thus hidden and cannot be seen from the upper side of the cantilever. Accordingly, when these cantilevers are used in SPM, the terminal end of the probe and the measurement point of the object to be measured cannot be simultaneously observed from an optical microscope for use in aligning the sample and the probe portion. Positioning alignment at the micrometer level of the point to be measured thus becomes difficult when the cantilever is set to the SPM apparatus.
Further, since the probe position is not ascertainable, it is not always possible to start the measurement from a desired region on the sample. Since it is manipulated so as to shift the measurement position by a small extent each time, it takes time before the measurement of such a desired region can be made. As a result, a longer time is necessary until the completion of the measurement. Also in some cases, the resolution may be degraded during the scanning for alignment due to the adhering of dust or the like or to the thickening of the probe portion by abrasion with the sample.
In this regard, the probe portion of those cantilevers as shown in FIGS. 1C and 1D is located at the terminal end of free end of the lever portion; and the probe portion can be easily brought near to a region to be observed on the sample. In short, it is easy to use. Both of these constructions, however have problems to be mitigated. In particular, since acuteness of the terminal end of the probe of the cantilevers shown in FIG. 1C cannot go beyond the resolution of photolithography, it is difficult to achieve a sharp terminal end of the probe which is important in SPM measurement at high resolution. Specifically, it is not easy to achieve a radius of curvature of 50 nm or less for the terminal end of the probe. Further, since the probe portion is in the shape of a triangular flat plate, the probe portion lacks rigidity. When a large force is placed between the sample and the probe portion, deformation occurs not only in the lever portion, but also at the triangular flat plate of the probe portion whereby measurement becomes unstable. If such a cantilever is used in the type of SPM measurement method where the cantilever is kept oscillated, a peak due to a separate oscillation mode occurs in a frequency region relatively near the fundamental frequency. The measurement becomes unstable or is degraded in sensitivity.
Further, the probe portion 108 of the cantilever shown in FIG. 1D is a bulk probe portion consisting of silicon. When compared with the other cantilevers shown in FIGS. 1A to 1C, the probe portion becomes heavier for the same probe height. This causes a difficulty in making a cantilever of which the cantilever length is short and the resonance frequency is high. In particular, its terminal end becomes structurally heavier so that the cantilever having a high resonant frequency becomes difficult to be designed.
Further, in SPM measurement, the probe portion of a cantilever is required to have an extremely acute tip to perform high resolution measurement. In this regard, of the probe portion 102 in the shape of a quadrangular pyramid shown in FIG. 1A, the tip is difficult to be terminated at a point theoretically because of its structure. It has a problem concerning acuteness of the probe portion. This is because the quadrangular pyramid has four ridgelines extending toward the terminal end of the probe and the four line segments do not theoretically cross each other at a point. Further, for the probe portion in the shape of a circular cone shown in FIG. 1B, it is also rather difficult to make the probe portion terminating at a point for a similar reason as the above, if a cone-shaped probe is regarded as resulting from the transition of a quadrangular pyramidal probe to a polygonal pyramidal probe
Furthermore, while SPM was used originally for the observation of a crystal sample surface or a deposited film surface, there has been an increasing need for SPM in recent years to measure the surface configuration of a sample (such as semiconductor IC device) having a larger irregularity for example of 100 nm to several xcexcm. There is a demand thus for further slenderness not only of the probe tip but also of the thickness of the probe portion away from the probe tip toward the lever side. In short, a probe portion having a high aspect ratio is demanded. This, however, is difficult to be achieved by the conventional cantilevers.
To eliminate the above problems, it is an object of the present invention to provide a cantilever for Scanning Probe Microscopy by which it is easy, before SPM measurement (scanning), to position the probe portion in alignment with the region to be observed on a sample and a SPM measurement at high resolution is possible, and which is suitable for high-speed scan measurement.
It is a further object of the invention to provide a cantilever for Scanning Probe Microscopy in which, as a result that it is made easier to position the probe portion in alignment with the region to be observed on a sample before SPM measurement (scanning), changes in the shape of probe portion due to wear of the probe portion or to adhering of foreign matter thereto are mitigated so that measurement at high resolution is possible in a stable manner for a longer time period.
It is another object of the invention to provide a cantilever for Scanning Probe Microscopy, having a probe portion of a high aspect ratio while structurally capable of achieving a steadily acute probe chip configuration.
It is another object of the invention to provide a cantilever for Scanning Probe Microscopy in which the rigidity of the probe portion is high and which operates steadily.
It is another object of the invention to provide a cantilever for Scanning Probe Microscopy, having a probe structure applicable to the range of low resonance frequencies to high resonance frequencies.
It is another object of the invention to provide a cantilever for Scanning Probe Microscopy, having a relatively short length which makes high-speed scanning measurement possible for those having a high resonance frequency.
These and other objects are described correspondingly to the respective aspects of the invention as follows. In particular, it is an object of a first aspect of the invention to provide a cantilever for Scanning Probe Microscopy in which the positioning alignment of the probe portion is easy and a drop in resonant frequency is less so that a high-resolution measurement is steadily made possible.
In accordance with the first aspect of the invention, there is provided a cantilever for Scanning Probe Microscopy, including: a support portion; a lever portion extended from the support portion; and a probe portion provided at a free end of the lever portion, wherein the probe portion is configured by two thin plates crossing each other in a manner facing each other, each having one side respectively being one of the different sides of V-like notch formed on the free end of the lever portion. By such construction, it is possible to achieve a cantilever for Scanning Probe Microscopy in which the probe portion is obtained as light in weight and high in rigidity so that the positioning alignment of the probe portion is easy and a drop in resonant frequency is less to make a high-resolution measurement steadily possible. The above object is thereby accomplished.
It is an object of a second aspect of the invention to provide a probe portion having a high aspect ratio in the cantilever for Scanning Probe Microscopy according to the first aspect.
In accordance with the second aspect of the invention, the two thin plates of the probe portion in the cantilever for Scanning Probe Microscopy according to the first aspect are respectively warped and curved toward the sides at which they face each other.
By such construction, the probe portion can be achieved as light in weight and high in rigidity and at the same time having a high aspect ratio where its tip has a steady acuteness. The above object is thereby accomplished.
It is an object of a third aspect of the invention to provide a probe portion which has a high aspect ratio and by which positioning alignment is even more easier in the cantilever for Scanning Probe Microscopy according to the first or second aspect.
In accordance with the third aspect of the invention, the apex of the probe portion is disposed at a position perpendicularly below the free end of the lever portion or at a position beyond the free end of the lever portion in the cantilever for Scanning Probe Microscopy according to the first or second aspect.
By such construction, the probe portion can be achieved as light in weight and high in rigidity and at the same time having a high aspect ratio with its tip having a steady acuteness and capable of more easily being positioned in alignment. The above object is thereby accomplished.
The objects of fourth to sixth aspects of the invention are to provide actual configuration of thin plates for forming the probe portion in the cantilever for Scanning Probe Microscopy according to the first to third aspects.
In accordance with the fourth aspect of the invention, the two thin plates constituting the probe portion are each triangular in the cantilever for Scanning Probe Microscopy according to any one of the first to third aspects. In accordance with the fifth aspect of the invention, the two thin plates constituting the probe portion are each quadrangular in the cantilever for Scanning Probe Microscopy according to any one of the first to third aspects. In accordance with the sixth aspect of the invention, the two thin plates constituting the probe portion are each sector-shaped in the cantilever for Scanning Probe Microscopy according to any one of the first to third aspects.
By such construction, the cantilever for Scanning Probe Microscopy can be achieved as reduced in weight with securing the rigidity at the probe portion and capable of preventing a drop in the resonance frequency. The above object is thereby accomplished.
It is an object of a seventh aspect of the invention to provide a construction of the cantilever for Scanning Probe Microscopy according to the first to sixth aspects of which the fabricating method is relatively easy.
In accordance with the seventh aspect of the invention, the probe portion and the lever portion in the cantilever for Scanning Probe Microscopy according to any one of the first to sixth aspects are monolithically formed from the same material.
By such construction, it is possible to achieve a cantilever for Scanning Probe Microscopy which can be made through a relatively easy fabricating process. The above object is thereby accomplished.
It is an object of an eighth aspect of the invention to provide an electrical conductive construction of the cantilever for Scanning Probe Microscopy according to the seventh aspect.
In accordance with the eighth aspect of the invention, the material for monolithically forming the probe portion and the lever portion is a conductive film in the cantilever for Scanning Probe Microscopy according to the seventh aspect.
By such construction, it is possible to achieve the cantilever for Scanning Probe Microscopy which has an electrically conductive lever portion and a probe portion. The above object is thereby accomplished.
It is an object of a ninth aspect of the invention to provide a construction of the cantilever for Scanning Probe Microscopy according to the first to sixth aspects of which room for designing is greater.
In accordance with the ninth aspect of the invention, the probe portion and the lever portion in the cantilever for Scanning Probe Microscopy according to any one of the first to sixth aspects are formed of different material from each other.
By such construction, it is readily possible to make wider the scope of design concerning the rigidity of the probe portion, and spring constant and resonance frequency, etc. of the lever portion. The above object is thereby accomplished.
It is an object of a tenth aspect of the invention to provide a construction capable of readily changing the characteristics of the probe portion and the lever portion in the cantilever for Scanning Probe Microscopy according to the first to ninth aspects.
In accordance with the tenth aspect of the invention, a film of a material different from the constituting material of the probe portion and the lever portion is formed on a surface of the probe portion and the lever portion in the cantilever for Scanning Probe Microscopy according to any one of the first to ninth aspects.
By such construction, it becomes possible to adjust hardness of the probe portion or to add conductivity to the lever portion and the probe portion without changing such characteristics of the lever portion as resonance frequency and spring constant, thereby achieving the cantilever of a higher added value. The above object is thereby accomplished.